1. Field of the Invention
The present invention relates to a process for smelting copper sulfide concentrates to extract blister copper.
2. Prior Art
As schematically depicted in FIG. 1, a continuous copper smelting apparatus comprised of a plurality of furnaces is hitherto known. The continuous smelting apparatus comprises three furnaces connected in series through launders 7 for flowing melt therethrough. Copper concentrates are smelted in a smelting furnace 1 and transported through the launder 7 to a separating furnace 2, where the melt is separated into immiscible upper and lower layers of slag S and matte M, respectively. The matte M, which contains copper as the main constituent, is siphoned out from the separating furnace 2 and transferred to the converting furnace 3 through the launder 7. In the converting furnace 3, iron sulfide and subsequently sulfur are removed by oxidation from the matte M, and blister copper C is obtained.
In each of the smelting furnace 1 and the converting furnace 3, lances 5, each having a double-pipe structure, are inserted through the furnace roof and attached thereto for vertical movement. Copper concentrates, oxygen-enriched air, flux, cold charge and so on are supplied into each furnace through the lances 5. The separating furnace 2 is an electric furnace, which is equipped with electrodes 6.
The blister copper C produced continuously in the converting furnace 3 is stored temporarily in a holding furnace 8, and then received in a ladle 9 which is conveyed by means of a crane 10 to the anode furnaces 4, and the blister copper C is poured thereinto through the inlet formed in the top wall. In the anode furnaces 4, the blister copper C is further oxidized and reduced into copper of greater purity, which is then cast into anode plates and is subjected to electro-refining.
In the smelting furnace 1 and the converting furnace 3, the fluxes supplied through the lances 5 help the formation of a fluid slag of an appropriate viscosity, which absorbs FeO or the like produced in the furnace to thereby improve smelting efficiency.
The slag S discharged from the separating furnace 2 is solidified, granulated, and used as cement filler material, subgrade materials or the like; whereas, as shown in FIG. 2, the slag discharged from the converting furnace 3, which contains a high proportion of calcium, is recycled to the smelting furnace 1.
The off-gases, exhausted from the smelting furnace 1 and the converting furnace 3, respectively, contain sulfur dioxide of a high gas strength, and in an acid plant 11, the sulfur dioxide is absorbed by water to produce sulfuric acid. Furthermore, in the waste liquid treatment in the acid plant, gypsum (CaSO.sub.4.2H.sub.2 O) is inevitably produced.
Thus, in the aforesaid copper smelting process, gypsum is produced in a predetermined proportion to the production of blister copper. Therefore, when gypsum is in low demand, the smelting process incurs high cost, and a large amount of gypsum must be disposed of.